I hate when its too muddy, one of the local trails near me actually has gates that they close to the parking lot if its too wet during the winter, problem is i think the guys seem to lazy to open em back up sometimes so its closed for like half the winter or at least thats what it feels like.
but the worst i've ever had was i showed up to the trail parking lot and there was a sign saying trails closed for controlled deer hunt, actually at the dh place near me the unwritten rule during hunting season is bikes only on sundays, at least we get the rest of the year.